1. Field of the Invention
The present invention relates to a printing apparatus for printing images using, a photosensitive unit such as a photosensitive drum. In particular, the present invention relates to a printer incorporating a paper-cutting mechanism to cut continuous recording paper into separate cut sheets for printing desired images on these cut sheets.
2. Description of the Related Art
A conventional printer of the above type is disclosed in JP-A-7(1995)-304220 for example. As shown in FIG. 7 of the accompanying drawings of the present application, the conventional printer has an image forming section provided with a photosensitive belt 90, a transfer unit 91 and a fixation unit 92. The printer also includes a paper holder 93 for accommodating a paper roll R. Continuous recording paper 94 is paid out from the paper roll R to be brought into contact with the photosensitive belt 90 by a plurality of feed rollers 95.
In the conventional printer, use is made of a sensor 96 and a cutter 97, each of which is arranged at a suitable location along the feeding path of the continuous paper 94. The sensor 96 is provided for detecting the passage of the continuous paper 94, while the cutter 97 is provided for cutting the continuous paper 94. More specifically, the sensor 96 is arranged to detect the passage of the leading portion of the continuous paper 94. Upon such detection, the continuous paper 94 is advanced a predetermined distance toward the photosensitive belt 90. Then, after the continuous paper 94 has been thus moved, the cutter 97 is operated to cut the continuous paper 94 to provide a cut sheet of a predetermined size.
The advantages of the conventional printer are as follows. Firstly, the recording paper 94 is a single elongated sheet when it is drawn out from the paper holder 93. Thus, the recording paper 94 will not suffer the problem of "double feed" which is liable to occur when initially separate cut sheets are used in place of the continuous paper 94.
Secondly, the continuous paper 94 is not allowed to maintain its continuous form but is cut into separate sheets by the cutter 97 arranged upstream from the photosensitive belt 90. With such an arrangement, the mechanisms of components arranged behind (i.e., downstream from) the photosensitive belt 90 are advantageously simplified, as in a specialized printer which is designed to deal with cut sheets only. This advantage can be better understood by considering the following case.
If the continuous paper 94 is not to be cut into separate cut sheets at all, additional devices, which would otherwise be unnecessary, may be required. The additional devices may include devices to detach the photosensitive belt 90 and the fixation unit 92 from the continuous paper 94 when the printing operation should be halted temporarily. Such detachment is needed for protecting the belt 90 from possible mechanical damage inflicted by the continuous paper 94, and for protecting the paper 94 from possible thermal damage inflicted by the fixation unit 92. The additional devices may also include a folding device for the continuous paper 94. The folding device may be disposed at the end of the feeding path for alternately folding the continuous paper 94, so that the discharged paper 94 is neatly accommodated in a stacker.
Though the conventional printer possesses the above advantages, it has been found disadvantageous in the following points.
In the conventional printer, the continuous paper 94 is cut into a separate sheet before the leading portion of the continuous paper 94 comes into contact with the photosensitive belt 90. Thus, the cut sheet separated from the continuous paper 94 needs to be transferred a certain distance until it comes into contact with the photosensitive belt 90. In this manner, the cut sheet tends to be improperly oriented (skewed for example) during the transfer to the photosensitive belt 90. When such improper transfer occurs, the cut sheet may fail to come into square contact with the photosensitive belt 90. Consequently, the printing operation may be started at an unintended portion of the cut sheet, and the resulting image printed on the cut sheet may unfavorably be slanted.